Micromechanical devices (also called microelectromechanical (MEM) devices, micromachined devices, and nanostructures) are micron scale three-dimensional objects constructed using semiconductor processing techniques. As used herein, the term micromechanical refers to any three-dimensional object that is at least partially constructed in reliance upon semiconductor processing techniques.
Micromechanical devices are utilized as fluid control devices. As used herein, the term fluid refers to either a gas or a liquid. Precise fluid control is important in many applications ranging from drug delivery to semiconductor processing equipment. FIG. 1 illustrates a prior art "gas stick" 20 used in semiconductor processing equipment. The gas stick 20 precisely controls a fluid in the form of a gas. The gas stick 20 includes a set of gas control components 22, which may include shut-off valves, pressure sensors, mass flow controllers, filters, purifiers, pressure gauges, and the like. Each gas control component 22 is mounted on a component substrate 24.
The gas stick 20 also includes a manifold substrate 26 including individual manifold segments 28. The manifold segments 28 of the manifold substrate define gas channels 30 through which a gas passes. More particularly, the gas is routed from the gas channel 30, into a gas control component 22, back to the gas channel 30, into another gas control component 22, and so on.
FIG. 2 illustrates a prior art manifold substrate 40 that may be used to construct a gas stick. The manifold substrate 40 includes individual manifold segments 42 connected by piping 44. Each manifold segment 42 includes a manifold segment face 46 with a first gas aperture 48 and a second gas aperture 50 to respectively receive and transmit a controlled gas. A gas control component (not shown) is mounted at each manifold segment 42 to process the received gas and then transmit the gas back to the manifold substrate 40. By way of example, FIG. 2 illustrates a manifold substrate configured to receive ten gas control components: six shut-off valves (SOV), two Mass Flow Controllers (MFC), one pressure sensor (PS), and one pressure regulator (PR). Observe that each gas control component requires its own manifold segment. Thus, the manifold substrate 40 consumes a relatively large space and is relatively expensive.
FIG. 3 is a side cross-sectional view of a prior art device including a fluid control component substrate 60 with an input port 62 and an output port 64. Mounted on the fluid control component 60 is a first micromechanical gas control component 66 in the form of a normally open proportional valve and a second micromechanical gas control component in the form of a pressure sensor 67. The gas control component 66 includes a membrane 68 and a membrane control chamber 70. Fluid 71 in the membrane control chamber 70 is selectively heated, thereby expanding the volume of the membrane control chamber 70, causing the membrane 68 to deflect and thereby obstruct fluid flow in the input port 62. The deflection of the membrane 69 associated with the pressure sensor 67 is used to measure the pressure of the controlled fluid.
Observe in FIG. 3 that the micromechanical gas control components 66 and 67 are parallel (mounted in the same horizontal plane) as the component substrate 60. In turn, the component substrate 60 is parallel (mounted in the same horizontal plane) as the manifold segment face 46. This configuration leads to a number of problems in the prior art.
The primary problem associated with this prior art configuration is that it exposes components 66 and 67 to stresses induced from sources other than the controlled fluid. For example, the components 66 and 67 are subject to mechanical or thermally induced mounting stress forces, generally illustrated with arrows 72. The mounting stress forces are due to the mechanical coupling between the components and the substrate, or are due to thermal expansion mismatch between the components and the substrate. In the case of the pressure sensor 67, these stresses are mistakenly processed as signals from the controlled fluid, leading to erroneous output signals.
The mounting stress forces can cause failure in the die attach material between the components and the substrate. In some cases, the mounting stress forces can actually break the fluid control components.
To avoid these problems, some silicon pressure sensors are mounted to a surface using a soft, compliant material, such as silicone or RTV. Soft materials are used in order to isolate the component from thermally or mechancially induced package stresses. Unfortunately, these materials are inappropriate for a large class of applications. In particular, these materials are inappropriate for use in the control and distribution of gases for semiconductor processing. In this context, the gases may be corrosive or toxic. The ideal attachment of the sensor to the substrate or package is hermetic. Hermetic seals are typically quite hard, and will transfer package stress directly to the sensor. As a consequence, alternative methods of mechanically isolating a fluid control component from its substrate must be used.
Semiconductor processing equipment also requires continued cleanliness of the fluid control components. The fluid control device must not corrode, nor generate particles that would affect the semiconductor fabrication process. This limitation eliminates virtually all soft, compliant materials from consideration as candidates for component attachment.
In view of the foregoing, it would be highly desirable to provide an improved technique for mounting fluid control components. Ideally, such a technique would provide relatively compact and efficient fluid control structures.